Process of treating and fractionating cracking-plant vapors



Sept. 18, 1928. 1,684,771

E. m. LESLIE ET AL PROCESS OF TREATING AND FRACTIONATING CRACKING PLANT VAPORS Filed May ll, 1923 720d M flemu Patented Sept. 18, 1928.

UNITED STATES PATENT OFFICE.

EUGENE IE. LESLIE AND EDWIN M. BAKER, OF ANN ARBOR, MICHIGAN.

PROCESS OF TREATING AND FRACTIONA'IING GRACKING-IELANT VAPORS.

Application filed May 11,

This invention relates to a process of treating and fractionating cracking-plant vapors, and more particularly to a process of treating the vapors coming from the cracking-coils of a vapor-phase cracking-plant.

In prior methods of cracking hydrocarbon and petroleum oils it has commonly been-the practice to condense the cracked vapors soon after the cracking operation, and to there- IO upon redistill the condensate .in order to obtain various desired products. This procedure provides no means for utilizing the heat present in the cracked vapors, and it also makes it necessary to employ additional heat l5 energy in re-distilling the condensed vapors. The necessity for providing additional stills for the re-distillation adds to the expense of installation and also of operation. Furthermore, the process of re-distillation in conventional cylindrical stills is objectionable in that the prolonged heating causes the polymerization of volatil olefin to high-boiling products, and thus a direct loss of valuable gasoline. In previous cracking-plant practice difiicult-ies resulting from the deposition of carbon and tarry substances in the condenser are encountered.

@ur invention has for its object the utilization of the heat contained in the vapors exiting from the cracking-coils, tubes, or vessels of a cracking-plant. Further objects of our invention are the provision of a method for utilizing this heat in the fractionation and separation and the cracked-vapors into the desired products, and to fractionate and separate so effectively that no re-distillation of the products is necessary before they are refined with sulfuric acid or other reagent. It is further .our object to provide a process that obviates and. avoids the difliculty ordinarily encountered and resulting from the deposition of carbon and tarry products in the condenser used to render liquid the crackedvapors. And it is a still further object of our invention to avoid the loss of valuable gasoline that results from the prolonged heating of volatil olefins in the conventional cylindrical still, which heating results in the polymerization of the low-boiling olefins to high-boiling substances. Further objects will appear hereinafter.

The invention in one of its preferred embodiments may be carried out in a form of apparatus illustrated in the accompanying drawing which forms a part of this specification. The figure of the drawing illus- 1923. Serial No. 638,176.

trates a plant for the treatment of crackingplant vapors and gases. I

In said drawing there is shown a carbon scrubber 1 of the usual construction, this scrubber serving to remove a portion of the carbon and tar from the vapors. A pipe 2 leads from the central axis of the scrubber to a vaporizer 3 provided with an upper packmg zone 4 and a lower packing zone 5. perforated tray 6 may be placed above the zone 4:, while beneath the zone 5 there is positioned a float 7 controlling a' balanced valve 8 that regulates the flow of residuum through a pipe 9 from the bottom of the vaporizer.

A fractionator 10 is mounted above the vaporizer and connected thereto by a short conduit 11. The fractionator is built to contain a suitable number of sections provided with nipples 12 for the purpose of causing liquids to collect and to permit liquids to descend and vapors to ascend. Each section is preferably filled with packing material 13 and is provided with an exit pipe 14 for liquid products, and if desired, with exit pipes 14* for vapor products. The pipes 14; are preferably connected to coolers, and the pipes 14 to condensers. A condenser 15 is placed above the fractionator to receive vapors and gases through a pipe 16 and to return condensed liquids through a pipe 17, to the top of the fraotionator. Uncondensed gases and vapors are led off through a pipe 18 to suitable absorbers wherein any condensable' vapors are recovered.

The invention in one of its preferred embodiments consists in treating the hot vapors from a vapor-phase oil cracking-plant in which they have been heated to a high temperature; for example, 500 C. to 600 C. In the cracking-plant, the vapors are decomposed and dissociated thermally to form various products, such as gasoline, hydro-carbons boiling higher than asoline, polymerized and tarry products, carbon and carbon-like substances, and gases (methane, ethylene, propylene, hydrogen, etc.). These hot vapors and gases are conducted into the scrubber 1,

wherein carbon and heavy tar are in part removed; and they are then passed into the vaporizer 3 in a superheated condition. They at once encounter the liquid that is running downwardly over the packing 4:. A state of equilibrium is approached, as a result of which new vapor and liquid phases are formed. A large portion of the descending liquid is revaporizeol, thus utilizing the heat in the entering vapors, and the heavier components of the entering vapors pass into the newly forming liquid phase. This liquid from the packing 4: flows downwardly over and through thepacking 5, where opportunity is given for approach to equilibrium and elimination of entrained Vapor. The liquid residuum collects at the bottom of the vaporizer and is regularly removed through the pipe 9.

The vapors and gases escaping from the zone 4 issue through the pipe 11 and enter the fractionator. As they ascend the fractionator a progressive fractionation takes place with the result that a sharp separation of products is obtained. Products may be removed from selected sections through the pipes 14;, preferably in the form of liquids. In case vapor products are to be removed they would be taken off at the upper part of the sections through the'pipes 14 The condenser 15 is preferably operated-to condense all of the condensable vapors and to return them to the fractionator. The gas that passes through the condenser is led off to a suitable absorber.

The various products obtained from the fractionator may comprise gasoline, naphtha, kerosene, and higher boiling distillates.

e various products will be found to be much more sharply cut, that is they will have a more restricted boiling point range, than the products obtained by processes in use heretofore. Products obtained from a lower section or sections of the fractionator may be sent back to be re-cracked.

While the process has been described with respect to the treatment of vapors obtained from a cracking-plant in which the cracking Was done by the vapor-phase method, it is pointed out that the process is also applicable to vapors obtained from other types of cracking processes. From whatever source the vapors are obtained they will be introduced into the vaporizer and treated substantially in the same manner as above set forth.

It will be seen that the process of our invention avoids a condensation of the vapors and a re-distillation thereof, since the vapors are directly led into an apparatus in which they are separated from carbon, tar, and heavier constituents, and thereupon directly fractionated. The heat of the Vapors, both latent and sensible, is therefore effectively utilized in the fractionating operation. The short time in which the vapors are maintained in a heated condition prevents any substantial polymerization of olefins. The entire plant is less expensive to build and operate than the plants necessary to operate according to the prior processes as previously outlined. A still further advantage of the process consists in the novel manner in which the carbon and tar materials are washed out of the vaporizer chamber and conveyed away without clogging up the ap paratus. It will therefore be apparent that we have achieved the objects of our invention by providing 'a process as described in the foregoing, together with a suitable apparatus for carrying it out.

As many apparently widely different embodiments of our invention may be made Without departing from the spirit thereof, it is to be understood that we do not limit ourselves to the embodiments described except as definedin the following claim.

We claim In a process of obtaining valuable products from mineral oil the steps which comprise conducting superheated hydrocarbon vapors from a vapor phase cracking plant into'the lower part of a fractionating column and effecting countercurrent contacting between such vapors and a liquid condensate, and refluxing to the upper part of said column a substantial portion of the vapors leaving said column, thereby providing liquid condensate for said countercurrent contactm Tnvtestimony that we claim the foregoing, we have hereuntoset our hands this 17th day of April, 1923. I

EUGENE H. LESLIE. EDWIN M. BAKER. 

